This invention relates to a mechanism for discriminating signature sets of abnormal total thickness from those of normal total thickness in a saddle wired bookbinding apparatus. An apparatus for saddlewired bookbinding is generally adapted to supply signatures from a plurality of signature feeders so that the signatures are stacked on a transfer saddle; transfer the resultant signatures to a stitcher i.e. signature sets, with pushers is provided on gathering chains moving along the saddle; stitch the backs of the signature sets to provide saddle-wired sets; and feed the saddle-wired sets to a three-sided trimming unit and there cut off the upper, lower and fore marginal portions thereof, whereby finished saddle-wired signatures are prepared.
An unnecessary signature is often supplied from a signature feeder, or a required signature is not supplied from a signature feeder. If an unnecessary signature is sent to the transfer saddle, the total thickness of the resultant signature set becomes larger than a predetermined total thickness thereof. If a necessary signature is not sent to the transfer saddle, more precisely, a necessary signature fails to be taken, the total thickness of the resultant signature set becomes smaller than a predetermined total thickness thereof. If such a signature set with an unnecessary signature included therein, or with a neccessary signature omitted is wired in that condition an inferior book results. Namely, unless such a signature set having an extra signature or lacking one or more signatures is removed before it has been stitched to the outside of the system of a regular flow of signature sets, an inferior saddlewired book is put on the market.
In a conventional apparatus for saddle-wired bookbinding, these problems are solved in the following manner. Namely, a signature set, which consists of a predetermined number of signatures supplied from signature feeders, and which is sent to a stitcher, is passed between a vertically-movable sensor wheel provided at the upper side of the stitcher and a lower sensor wheel opposed to the movable sensor wheel, to detect mechanically the movement of the upper sensor wheel, which moves as it turns upward simultaneously with the passage of the signature set between the sensor wheels, amplify this movement mechanically, set the stitcher so that a stitch arm thereof is not operated in certain cases, that is, in such a manner that a signature set having an abnormal total thickness is not stitched, and switch a deflector lever mechanically for introducing the signature set of an abnormal thickness from a passage, which leads to a three-side trimming unit, to the outside of the system and laying it on the similar signature sets already discharged from the regular passage.
In order to amplify a small quantity of movement of the sensor wheel mechanically, stop the movement of the stitch arm of the stitcher and switch the deflector lever in the above-described manner, it is necessary that the apparatus for saddle-wired bookbinding be formed in a very complicated construction. Namely, in order to carry out the above-mentioned operations, it is necessary to amplify and transmit the movement of the sensor wheel by driving various means, such as a lever, a rod and a crank. Moreover, it is extremely difficult and requires parts of a very complicated construction to time mechanically the actions of a stitcher operating means and a means for supplying a signature set to the three-side trimming unit since these means are disposed in different positions. In such an arrangement, breakage and wear of the parts of these means adversely affect the judment of the total thickness of a signature set. Therefore, judging of the total thickness of a signature set cannot be performed accurately.